Method of coking hydrocarbon oils



p 7, 1955 H. G. RUSSELL METHOD OF COKING HYDROCARBON OILS Filed May 11, 1950 INVENTOR HOWARD GENE PussELL BY M/ww 23Cob u ATTORNEYS Patented Sept. 27, 1955 2,719,115 NIETHOD OF COKING HYDROCARBON OILS Howard Gene Russell, Hammond, Ind., assignor to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application May 11, 1950, Serial No. 161,407 1 Claim. (Cl. 2028) My invention relates to improvements in the coking of hydrocarbon oils. Particularly it relates to a fluidized coking process capable of operating at an unusually high coking temperature in an operation employing separate oil contacting and coking reaction zones.

According to my invention, a hydrocarbon oil of the usual coking charge type, c. g. a heavy reduced crude, is contacted with a body of adsorbent coking particles maintained in a fluidized state in a vertically enlarged contact vessel. The contacting is effected at a relatively moderate coking temperature, e. g. about 800 to 925 F., for a short time factor. Steam is introduced to the bottom of the body of coke particles, and vapors stripped from the coking charge stock are removed with the steam overhead. A stream of coke particles with adsorbed oil is continuously and rapidly passed from the contact vessel to a coking chamber where the coke particles are maintained in a fluidized state and at a high coking temperature; e. g., about 1000 to 1250 F., by introducing a mixture of flue gas and air to the bottom of the chamber. A portion of the coke make thus is consumed by combustion with air in producing the high coking temperature of the coking chamber. The hot coke particles are withdrawn from the bottom of the coking chamber and a portion is recycled to the contact vessel. Flue gas and cracked vapors are taken overhead from the coking chamber to a lower section of an absorber tower and are passed upwardly against a descending stream of fresh coking charge stock charged to an upper section of the absorber tower, so that the liquid products of the coking reaction are scrubbed out together with entrained coke fines. The fresh oil stream is removed from the bottom of the absorber tower, raised to the moderate coking temperature level, as by passage through a conventional fired heater, and the preheated oil stream is discharged into the body of fluidized coke particles contained in the contact chamber.

Thus my invention provides a cyclic coking process in which preheated oil feed is separately contacted with adsorbent hot coke particles for a suflicient time for the surface of the coke to become saturated with coke and pitch producing constituents of the charge oil. Under the conditions of coking temperature and low partial pressure due to the stripping and fluidizing steam introduced beneath the body of coke particles in the contact chamber, all but the-heavy ends of the feed stock are stripped out and removed overhead as a vapor stream to a conventional fractionation system. The coke particles with the adsorbed heavy ends gravitate against the flow of fluidizing and stripping steam through a stand pipe to a separate coking chamber. Here sufiicient time at high coking temperature produced by the combustion of a limited amount of the coke yield in the lower portion of the coking chamber is provided to complete the coke formation.

One of the serious problems in coking hydrocarbon oils is the problem of supplying suflicient heat economically to the coking reaction in order to produce high yields of liquid distillate products suitable for catalytic cracking charge stocks with a minimum production of residuum in the form of coke. It is diflicult to preheat the usual black oil charging stock to a high enough temperature to obtain economically attractive yields. Thus the practical limit on black oil heater outlet temperatures is generally about 925 F., although in some instances as high as about 975 F., due to coking within the tubes or coils of the heater. It is diflicult to supply additional heat to the coking reactor by other means. Thus a superheated heat-carrier fluid, e. g. steam or the fluidizing medium in the case of a fluidized coking operation, may be employed but the large quantities of fluid required seriously decrease capacity, or conversely increase equipment size, and result in overloading the fractionation equipment to an extent making the operation uneconomic.

My invention provides a method where the operation is in eifect conducted stepwise, with the initial contacting of the oil charge stock with fluidized adsorbent coke particles so as to prevent internal wall and reactor coking. The contacting is effected at conventional coking temperatures but before the coking reaction has had time to proceed substantially, the heavy oil bearing coke particles are rapidly passed to a separate reaction chamber. The reaction is completed at a very high temperature induced by partial combustion of the coke product. The size of the equipment is reasonable because separate smaller and less expensive vessels are employed. The oil product fractionating equipment is not overloaded because the flue gases of the coking chamber do not contact or mix with the bulk of the oil vapors which are produced and separately removed from the first contact vessel. The relatively small amount of cracked vapors produced in the high temperature coking reaction are scrubbed out of the flue gas mixture by passing the mixture in countercurrent contact with the fresh oil charge in an absorber tower prior to its introduction to the contact chamber. The flue gases can be released to the atmosphere because of their usually low cracked gas content or may be recovered for recycling if desired. The absorber operation has the additional advantage of providing preheat for the fresh oil charge by direct heat exchange. The condensible products of the coking reaction recovered in the absorbing operation are recycled to the contact vessel with the fresh oil feed.

My invention will be further described with reference to the accompanying drawing which illustrates diagrammatically the combination of contacting, reaction, absorbing and heat equipment that may be employed.

. The coking charge stock in the flow plan of the drawing is introduced to absorber 10 through line 11. In absorber 10 it passes in countercurrent contact with hot gases from coking chamber 12 which are introduced to absorber 10 by means of connection 13. Intimacy of contact is promoted by staggered baffles 14 or other conventional mixing arrangements. The scrubbed gases are taken from the top of absorber 10 through line 15. The coking charge plus absorbed hydrocarbons and coke fines are withdrawn from the bottom of absorber 10 through line 16, and the stream is charged by pump 17 to heater 18.

The preheated charge stream is introduced by means of connection 19 into contactor 20. A body of coke particles is maintained in contactor 20, and even distribution of the charge stream is obtained by dispersion nozzles 21. The contactor 20 is maintained at a moderate coking temperature, e. g. 800 to 925 F., and the residence time of oil within the contactor 20 is short. Under these conditions, the heavy ends of the coking charge stock are selectively adsorbed on the surface of the coke particles maintained within the contactor 20 while the lighter ends are vaporized and removed overhead through line 20a to a conventional fractionating system for recovery of distillate gas oil and coker gasoline. Stripping and fluidizing steam are introduced at the bottom of contactor 20 through connection 22.

A stream of coke particles bearing the adsorbed heavy ends of the coking charge stock is continuously and rapidly passed through stand pipe 23 under control of slide valve 24 into coking chamber 12. The coking chamber 12 advantageously is bafiied by a series of horizontal perforated baflles 25 in order to provide a number of contact zones. The entire body of coke particles in the coking chamber 12 is maintained in a fluidized state and is heated to a high temperature by introduction of a mixture of flue gas and air at the bottom of the chamber as by connection 26. The amount of air in the flue gas is regulated so as to burn a part of the coke produced in the thermal reaction of the adsorbed heavy hydrocarbons on the coke particles. For example a high coking temperature of about 1200 F. is maintained in the body of coke particles by regulating the oxygen content of the fluidizing mixture at about 3 to per cent oxygen. The hot flue gas plus cracked hydrocarbon vapors and a small amount of entrained coke fines produced in the thermal reaction pass from the coking chamber 12 by means of connection 13 to the bottom of absorber 10. The net coke make is withdrawn from the coking chamber 12 as a stream of particles through stand pipe 27 under control of valve 28 into hopper 29. A water spray system advantageously is installed at 30. A portion of the net coke make is recycled by means of line 311 to the reaction system to maintain an adsorbent body of coke particles in contactor 20. Advantageously pneumatic lift as by steam or other inert gas is employed by injection through connection 32.

Ordinarily it is very diflicult to maintain a body of coke particles in discrete form and in a fluidized condition so that pitch and coke formation occurs on the surface of the coke particles rather than on the walls and the exposed metal surfaces of the reactor. Under coking conditions, the particles tend to agglomerate so that the entire bed solidifies and the process must be shut down to clean out the reactor. In operation according to my invention, where the oil is separately contacted with the adsorbent coke particles at a short time factor and the coke particles with adsorbed heavy hydrocarbons are rapidly removed to a separate chamber Where very high temperature and a high degree of fiuidization are maintained by burning a portion of the net coke make, the danger of losing fluidization of the coke bed is minimized.

A high rate of through-put is obtained by rapid coke circulation, and a high yield of liquid distillate products is produced because of the stepwise operation and unusually high coking temperature in the separate coking chamber. Operation is continuous without necessity of intermittent shut-down for the costly and laborious process of removing a coke batch from a reaction chamber. The heavy pitch forming and coking materials are selectively adsorbed on coke particles which are rapidly circulated through the contacting and reaction system and are easily removed continuously from the system.

I claim:

The method of coking hydrocarbon oils which comprises contacting a body of coke particles with a coking charge stock in a vertically enlarged contact vessel at a moderate coking temperature of the order of about 800 to about 925 F. for a suflicient time to strip all but the heavy ends of the charge stock and to saturate the surface of the coke particles with the remaining heavy hydrocarbons, maintaining the body of coke particles in a fluidized state by introducing steam to the bottom of the contact vessel, rapidly passing a stream of the coke particles and adsorbed heavy hydrocarbons from the contact vessel to a separate coking chamber so that the residence time of the hydrocarbons in the contact vessel is shorter than that required for coking the adsorbed hydrocarbons, maintaining the coke particles in the coking chamber in a fluidized state and at a high coking temperature of the order of about 1000 to about 1250 F. by introducing a mixture of flue gas and air at the bottom of the chamber, maintaining the coke particles in the coking chamber for a suflicient time to complete the coking reaction of adsorbed hydrocarbons, withdrawing coke particles from the chamber, recycling a portion at least of the coke particles to the contact vessel, passing flue gas and cracked vapors from the coking chamber to the lower section of an absorber tower, charging a fresh coking charging stock to the upper section of the absorber tower, removing vapors overhead from the absorber tower, removing an oil stream from the bottom of the absorber tower, whereby cracked vapors produced in the coking chamber are scrubbed out of the fiue gas mixture and are removed from the absorber tower in said oil stream, introducing the preheated oil stream into the body of fluidized coke particles in the contact vessel, and removing oil vapors from the contact vessel.

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